The present invention relates to a method and system for arranging a common line signal network through an ISDN (Integrated Service Digital Network) in a switching network in which a signal is transferred between switching stations through a leased line in a common channel signalling manner. More particularly, the invention relates to a method and a system for alternating a common channel signal path using the ISDN in a common channel signal network in which a signal is transferred through a leased line.
The conventional local switching network includes local switching stations and leased lines connecting the local switching stations. For using the leased lines, the contract is made on a line number and a using period. Recently, there has been a strong desire for expanding the service inside of one switching station to that between the switching stations. For achieving the service between the switching stations, a common channel signalling system has been used. The common channel signalling system is designed to transfer a signal between switching stations through a common signal line provided independently of a speech channel. The system thus makes it possible to transfer a signal during speech as well as without any concern with a call. If the switching network employs the conventional leased lines and a common channel signalling system for transferring a signal between switching stations, the network is designed to transfer a signal between switching stations by allocating a specific channel of the leased lines to a common channel signalling path. This kind of common channel signalling system has been disclosed in Japanese patent application laid-open No. JP-A-61-10347.
As described above, the foregoing conventional technology is designed so that a switching station allocates a specific channel of the leased lines to an object switching station in a fixed manner. Hence, if the switching station has only a small number of lines, the conventional technology lowers the efficiency of use of the leased lines.